package com.ouyu.im.utils;

import java.net.Inet4Address;
import java.net.UnknownHostException;
import java.util.HashSet;
import java.util.Random;
import java.util.Set;

/**
 * @Author fangzhenxun
 * @Description  雪花算法工具类
 **/
public class SnowflakeUtil {

    /** 时间部分所占长度 */
    private static final int TIME_LEN = 41;
    /** 数据中心id所占长度 */
    private static final int DATA_LEN = 5;
    /** 机器id所占长度 */
    private static final int WORK_LEN = 5;
    /** 毫秒内序列所占长度 */
    private static final int SEQ_LEN = 12;

    /** 定义起始时间 2015-01-01 00:00:00 */
    private static final long START_TIME = 1420041600000L;
    /** 上次生成ID的时间截 */
    private static long LAST_TIME_STAMP = -1L;
    /** 时间部分向左移动的位数 22 */
    private static final int TIME_LEFT_BIT = 64 - 1 - TIME_LEN;

    /** 自动获取数据中心id（可以手动定义 0-31之间的数） */
    private static final long DATA_ID = getDataId();
    /** 自动机器id（可以手动定义 0-31之间的数） */
    private static final long WORK_ID = getWorkId();
    /** 数据中心id最大值 31 */
    private static final int DATA_MAX_NUM = ~(-1 << DATA_LEN);
    /** 机器id最大值 31 */
    private static final int WORK_MAX_NUM = ~(-1 << WORK_LEN);
    /** 随机获取数据中心id的参数 32 */
    private static final int DATA_RANDOM = DATA_MAX_NUM + 1;
    /** 随机获取机器id的参数 32 */
    private static final int WORK_RANDOM = WORK_MAX_NUM + 1;
    /** 数据中心id左移位数 17 */
    private static final int DATA_LEFT_BIT = TIME_LEFT_BIT - DATA_LEN;
    /** 机器id左移位数 12 */
    private static final int WORK_LEFT_BIT = DATA_LEFT_BIT - WORK_LEN;

    /** 上一次的毫秒内序列值 */
    private static long LAST_SEQ = 0L;
    /** 毫秒内序列的最大值 4095 */
    private static final long SEQ_MAX_NUM = ~(-1 << SEQ_LEN);


    /**
     * @Author fangzhenxun
     * @Description  生成雪花id
     * @return long
     **/
    public synchronized static long nextId(){
        long now = System.currentTimeMillis();

        //如果当前时间小于上一次ID生成的时间戳，说明系统时钟回退过这个时候应当抛出异常
        if (now < LAST_TIME_STAMP) {
            throw new RuntimeException(String.format("系统时间错误！ %d 毫秒内拒绝生成雪花ID！", START_TIME - now));
        }

        if (now == LAST_TIME_STAMP) {
            LAST_SEQ = (LAST_SEQ + 1) & SEQ_MAX_NUM;
            if (LAST_SEQ == 0){
                now = nextMillis(LAST_TIME_STAMP);
            }
        } else {
            LAST_SEQ = 0;
        }

        //上次生成ID的时间截
        LAST_TIME_STAMP = now;

        return ((now - START_TIME) << TIME_LEFT_BIT) | (DATA_ID << DATA_LEFT_BIT) | (WORK_ID << WORK_LEFT_BIT) | LAST_SEQ;
    }


    /**
     * 获取下一不同毫秒的时间戳，不能与最后的时间戳一样
     */
    private static long nextMillis(long lastMillis) {
        long now = System.currentTimeMillis();
        while (now <= lastMillis) {
            now = System.currentTimeMillis();
        }
        return now;
    }

    /**
     * 获取字符串s的字节数组，然后将数组的元素相加，对（max+1）取余
     */
    private static int getHostId(String s, int max){
        byte[] bytes = s.getBytes();
        int sums = 0;
        for(int b : bytes){
            sums += b;
        }
        return sums % (max+1);
    }

    /**
     * 根据 host address 取余，发生异常就获取 0到31之间的随机数
     */
    private static int getWorkId(){
        try {
            return getHostId(Inet4Address.getLocalHost().getHostAddress(), WORK_MAX_NUM);
        } catch (UnknownHostException e) {
            return new Random().nextInt(WORK_RANDOM);
        }
    }

    /**
     * 根据 host name 取余，发生异常就获取 0到31之间的随机数
     */
    private static int getDataId() {
        try {
            return getHostId(Inet4Address.getLocalHost().getHostName(), DATA_MAX_NUM);
        } catch (UnknownHostException e) {
            return new Random().nextInt(DATA_RANDOM);
        }
    }


    public static void main(String[] args) {
        Set ids = new HashSet();
        long start = System.currentTimeMillis();
        for (int i = 0; i < 500; i++) {
            System.out.println(i+ "-->" +nextId());
        }
        long end = System.currentTimeMillis();
        System.out.println("共生成id[" + ids.size() + "]个，花费时间[" + (end - start) + "]毫秒");
    }
}
